The invention relates to an apparatus at a spinning preparation machine, especially a flat card, roller card or the like, having a roller, for example a cylinder, which has a cylindrical clothed peripheral surface having at least one clothed and/or unclothed movable or stationary machine element located opposite the roller clothing and spaced radially therefrom, and having two fixed side panels, on which work elements, e.g. sliding bends for revolving flat bars, stationary carding elements, roller coverings, are mounted.
In a known apparatus, at least two measuring elements for detecting variables linked to the dimensions of the roller are provided, the measuring elements being connected to an electronic open-loop and closed-loop control device and a first measuring element being in the form of a temperature probe for the temperature of the roller surface and a second measuring element being in the form of a rotational speed sensor for the speed of the roller.
The effective spacing of the tips of a clothing from a machine element located opposite the clothing is called the carding nip. The latter element can also have a clothing, but could instead be formed by a casing segment having a guiding surface. The carding nip is a determining factor for the quality of carding. The size (width) of the carding nip is a fundamental machine parameter, which shapes both the technology (the fibre processing) and also the running performance of the machine. The carding nip is set to be as narrow as possible, (it is measured in tenths of a millimeter), without running the risk of a “collision” between the work elements. To ensure that the fibres are processed evenly, the gap must be as uniform as possible across the entire working width of the machine.
The carding nip is influenced particularly by the machine settings on the one hand and by the condition of the clothing on the other hand. The most important carding nip of the revolving flat card is located in the main carding zone, i.e. between the cylinder and the revolving flat assembly. At least one of the clothings adjoining the work spacing is in motion, more often than not both. In order to increase the production of the carding machine, efforts are made to select the operating speed of rotation and the operating speed of the moving elements as high as the technology of fibre processing will allow. The work spacing changes in dependence on the operating conditions. The change takes place in the radial direction (starting from the axis of rotation) of the cylinder.
In carding, ever larger amounts of fibre material are being processed per unit of time, which involves higher speeds of the work elements and higher installed capacities. With the work surface remaining constant, increasing throughput of fibre material (production) leads to greater generation of heat owing to the mechanical work. At the same time, however, the technological carding result (sliver uniformity, degree of cleaning, reduction of neps etc.) is continually being improved, which requires more active surfaces engaged in carding, and settings of these active surfaces closer to the cylinder (tambour). The proportion of synthetic fibres to be processed is continually increasing, with more heat, compared with cotton, being produced as a result of friction from contact with the work surfaces of the machine. The work elements of high-performance carding machines are today fully enclosed all round in order to comply with the high safety standards, prevent particle emission into the spinning works environment and minimise the need for maintenance of the machines. Gratings or even open, material-guiding surfaces that allow exchange of air belong to the past. The circumstances described appreciably increase the input of heat into the machine, whereas there is a marked decrease in the discharge of heat by means of convection. The resulting increased heating of high-performance carding machines leads to greater thermoelastic deformations, which have an influence on the set spacings of the active surfaces owing to the uneven distribution of the temperature field: the distances between cylinder and card top, doffer, fixed card tops and separation points decrease. In an extreme case the set nip between the active surfaces can close up completely as a result of thermal expansion, so that components moving relative to one another collide. The high-performance card concerned suffers considerable damage. Moreover, in particular the generation of heat in the working region of the card can lead to different thermal expansions when the temperature differences between components are too large.
Owing to the heat input under production conditions, the cylinder heats up more than the side panel. By using different materials for cylinder and side panel, the change in carding nip under production conditions can be substantially compensated. This is the case, for example, when the warming ΔT of the cylinder is approximately double the value of the warming ΔT of the side panel. When using different materials, a problem arises in particular when there are temperature differences that act on the machine from the outside, and the warming of the cylinder no longer corresponds to the calculated value of the side panel, e.g. double the value. Large changes in the carding nip are the result in particular of fluctuating external temperatures, because these act in equal measure on the cylinder and the side panel and then the carding nips change owing to the different coefficients of expansion of the materials used. Especially when the machine is at a standstill, big differences can occur during set-up operations as a function of the ambient temperature. For the machine operator, these changes of distance are imperceptible and the outcome of the set-up can consequently vary considerably. Even during operation of the machine, different ambient temperatures can lead to different carding nips and hence to different results in the product. Since the adjustments to the drive elements around the cylinder are performed substantially manually, the times from adjustment to start-up of the machine or to a quality evaluation are in some cases considerably far apart. Extreme temperature differences can thus lead both to dangerously narrow and to large carding nips, with the corresponding disadvantages.
In the case of a known apparatus (DE 29 48 825C), the diameter of the cylinder in the unreformed state (i.e. in practice before start-up of the machine and at room temperature) is designated D, whilst the diameter (indicated by a dot-dash line) of the cylinder in a state deformed by the influence of centrifugal force and/or the effect of heat is designated D+ΔD. On the basis of the increase in diameter ΔD, the distance between the cylinder surfaces in the underformed state, provided that a co-operating cylinder is not deformed, would be reduced by
            Δ      ⁢                          ⁢      D        2    ⁢      :  an assumption that in many cases represents a good approximation. If the distance a in the underformed state of the cylinder were selected to be optimum, the distance
  a  -            Δ      ⁢                          ⁢      D        2  obtaining while the cylinder is in its deformed state, would lie below the admissible limit, which would be very dangerous. It is proposed that both the influence of the rotational speed of the cylinder and the influence of warming are taken into account. For that purpose, a rotational speed sensor, which detects the rotational speed of the axle of the tambour, and a temperature sensor, which detects the temperature of the surface of the cylinder, are provided. These elements are connected by corresponding leads to the control device for actuating means, the control device being pre-programmed both in respect of the direct correlation between the diameter D of the tambour and its rotational speed and the direct correlation between the diameter and the temperature of the surface of the tambour casing. Allowances are thus made for both influences by the control device, which supplies electrical signals to the actuating means, which enlarge the spacing between the cylinders. The drawback is that only the changes in the diameter of the roller can be calculated. A further disadvantage is that the changes in diameter of just the one roller can be calculated, and not of the counter-element adjoining the carding nip.
It is an aim of the invention to produce an apparatus of the kind mentioned at the beginning, which avoids or mitigates the said disadvantages, which in particular allows an actual carding nip to be determined at any desired point in time and permits a comparison with a preset carding nip (reference value). A further objective is to adjust the carding nip as a function of temperature and rotational speed measurements to a desired value.